There has been recently developed a high density information recorded disc, i.e. a video disc, in which the recorded information is in the form of a surface relief pattern formed along a spiral path or track in a major surface of the disc. For a capacitive electronic disc (CED) the surface of the disc is conductive. The disc is played with a conductive stylus which follows the track on the surface of the disc. In order to reduce frictional forces and reduce wear of the stylus and/or disc, the disc is preferably coated with a thin layer, about 200 Angstroms thick, of a lubricant.
U.S. Pat. No. 4,309,456 to Brian E. Lock, issued Jan. 5, 1982, entitled "Method and Apparatus For Coating Recorded Discs With A Lubricant" describes a method and apparatus for applying a thin coating of lubricant to a disc. The apparatus described in this patent includes an atomizer for forming fine particles of the lubricant and a flow of air for carrying the lubricant particles from the atomizer to nozzles in a coating chamber. The disc passes through the chamber and across the nozzles which direct the flow of lubricant particles onto the major surfaces of the disc. Although this patent shows the disc passing through the coating chamber in an upright position with the nozzles directing the flow of the lubricant particles in a horizontal direction against the major surface of the disc, the disc can pass through the coating chamber horizontally with one major surface facing upwardly and a nozzle directing the flow of the lubricant particles vertically downwardly onto the surface of the disc. The disc would then be turned over to coat the other surface.
In order to insure that the desired amount of lubricant is being coated on the disc, it is desirable to determine the presence and quantity of the lubricant particles delivered by the nozzle on a continuous basis. Also, this determination must be made at the nozzle end of the coating apparatus rather than at the atomizer where the lubricant particles are generated, because there could be some problem in the line between the atomizer and the nozzle which would affect the flow of the lubricant particles to the nozzle.